Tartary Buckwheat and Fagopyrism

“Fagopyrism” is photosensitization caused by the ingestion of buckwheat (usually by livestock). While redness and itching of lightly-pigmented skin are the common symptoms, digestive upset, neurological disorders, and death have been reported. If the affected animal is kept shaded, symptoms usually disappear within days. The toxic compounds are a group of polyphenols, collectively called “fagopyrin,” which are formed when precursors are illuminated by wavelengths in the yellow-orange part of the visible spectrum. In both common and Tartary buckwheat, fagopyrin is most concentrated in leaves. Levels in seeds are low, and much of that fagopyrin is concentrated in the hulls.

“Fagopyrism” is photosensitization caused by the ingestion of buckwheat. Symptoms have most often been reported after exposure to sunlight of albino or partially-pigmented livestock (swine, cattle, horses, sheep, rabbits, or rabbits) that had consumed common buckwheat as forage. Bruce (1917) described behavior of Yorkshire (white) pigs that had grazed on common buckwheat in bloom: “They would try to jump out of the enclosure, jump into the air with all four feet off the ground, shake their heads and squeal, then poke their heads against the pen or under a log, then lie quiet for three or four minutes when they would begin again. At times their hind legs were partially paralyzed.” More common symptoms are erythema, slight swelling, and itching of exposed unpigmented skin or mucous membrane—particularly on the head and ears. However, fagopyrism can also cause digestive upsets, convulsions, paralysis, or death. If affected animals are moved into shade, recovery generally occurs within a few days.

According to Chick and Ellinger (1941), green buckwheat plants, flowers, seeds, straw, stubble, and chaff had all been implicated in cases of fagopyrism. Experimenting with white rats, these authors determined that in common buckwheat the toxic agent was most concentrated in young flowers. Administered as a single dose or as 5 or 13 daily doses, a cumulative total of 0.25g of dried flowers per 100g body weight could cause symptoms. Sensitivity could persist for several weeks after the final dose. However, a daily dose of 0.01g per 100g could be administered indefinitely without toxic effect. While consumption of whole seeds could trigger fagopyrism, the authors found that dehulled groats did not.

Chick and Ellinger (1941) tested the effect of light of varying intensity, duration, and wavelength on skin sensitivity. They found that the most effective radiation was in the yellow-orange portion of the visible spectrum (i.e., 540-610 mµ). The authors tested many solvents to extract the active agent from dried buckwheat flowers, and achieved almost total separation with a mixture of 90 percent methanol and 10 percent glacial acetic acid.
This active ingredient was subsequently identified as a polyphenol compound, which was named “fagopyrin.” Fagopyrin is classified as a naftodianthrone, and closely resembles hypericin, an active agent in St. Johns wort. Hinneburg and Neubert (2005) employed a 23 factorial design to study the effects of temperature, duration, and solvent concentration on the extraction of fagopyrin from dried herbage of common buckwheat. Extraction was more effective in 70 percent ethanol than in 30 percent ethanol; at the former concentration, extraction was more effective at 60ºC than at 25ºC. Extending extraction time from two to 24 hours did not significantly increase the yield of fagopyrin, nor did duration interact significantly with the other variables. The authors noted that desirable flavonoids such as rutin could be extracted with 30 percent ethanol, thereby minimizing the concentration of fagopyrin in the product. Conversely, extracts enriched in fagopyrin have potential as sensitizers of photodynamic therapy. Such extracts have demonstrated light- and concentration-dependent inhibition of tyrosine kinase and serine/threonine kinase, a possible method of suppressing proliferative cell growth in tumors (Tavčar Benković et al., 2014).

Eguchi et al. (2009) devised a method to quantify fagopyrin content in buckwheat by HPLC, as an alternative to ultraviolet-visible photometry. Because of the retention of quantities of chlorophyll in extracts, the latter method tended to overestimate concentrations of fagopyrin. In extracts of samples from ‘Miyazakiootsubu’ common buckwheat and ‘Rotundatum’ Tartary buckwheat, the authors found three peaks corresponding to fagopyrin and its derivatives. All three peaks were integrated to estimate fagopyrin concentrations in flowers, leaves, and stems (at early flower) and hulls and groats (at maturity). The common and Tartary buckwheat flowers contained 0.64 and 1.84mg per g, respectively. Common and Tartary buckwheat leaves contained 0.39 and 1.06mg per g, respectively. Stems of Tartary buckwheat contained 0.11mg per g; all other samples contained less than 0.05mg per g.

Employing modifications of Eguchi’s analytical methods, Stojilkovski et al. (2013) reported fagopyrin concentrations in leaves and whole seeds of Tartary buckwheat grown at 2700m in Sichuan, China: 0.512 and 0.068mg per g, respectively. Those authors reported that the concentrations in leaves of common buckwheat from various sources ranged from 0.322 to 2.319mg per g. Two samples of leaves of F. cymosum contained 0.936 and 0.947mg per g. No data were presented from seeds of either of those species.

Using HPLC, Tavčar Benković et al. (2014) isolated eight fluorescent extracts from common buckwheat. Upon excitation at 330 nm, their optimal emission wavelengths were 590 nm. The authors calculated the elemental composition of six resolved peaks, and assigned molecular structures to three of these fagopyrins. The authors also reported that only invisible proto-fagopyrins existed in the dried buckwheat herbage, which had been stored under illuminated conditions for three years. Only when dissolved and then exposed to light were these compounds converted to fagopyrins (a process slowed under acidic conditions).

Kočevar Glavač and co-workers (2017) measured concentrations of total fagopyrins during the production of roasted Tartary buckwheat groat tea. Dry samples of raw seeds, steamed whole seeds, the steamed seeds after de-hulling (i.e., groats), and the groats after roasting were ground, extracted with methanol, and analyzed by HPLC. (These were the same samples whose levels of rutin and quercetin are reported in the section on FLAVONOIDS AND ANTI-OXIDANT PROPERTIES. ) Raw grains contained 53.7µg fagopyrin per gram dry weight. The steamed grains contained 17.1µg/g; the dehulled steamed grains contained 3.35µg/g. Three lots of roasted groats contained between 3.06 and 15.85µg of fagopyrin per gram dry weight. Larger fragments of the detached hulls contained between 7.76 and 7.92µg/g; in contrast, the concentration of fagopyrin in fine hull fragments exceeded 58µg per gram dry weight.

Kočevar Glavač and co-authors also reported concentrations of total fagopyrins during production of all-Tartary buckwheat yeast bread (details in FLAVONOIDS AND ANTI-OXIDANT PROPERTIESproperties). Dry samples of whole seeds, semolina, flour, dough from that flour, and the baked bread were analyzed. In the unmilled seed, the concentration of fagopyrin was 38.1µg per g. The semolina contained only 4.84µg per gram; in contrast, the flour contained 40.2µg per gram. The dough and baked bread contained concentrations of total flavonoid similar to the flour—39.1µg and 34.4µg per gram dry weight, respectively.